1. Field of the Invention
The present invention relates to an intravenous catheter set that is used in medical treatment, for example, in drip infusion, in blood transfusion, in dialysis and in like treatments.
2. Description of the Prior Art
A catheter tube of an intravenous catheter set is inserted into a blood vessel of a patient so that, through such catheter tube, a necessary medical treatment such as: injection of a medicine into the patient's blood vessel; continuous administration of nutriment to the patient; blood transfusion and/or dialysis necessary for the patient; and like treatments is conducted.
The catheter tube of a conventional type is constructed of a polytetrafluoroethylene tube or a polyurethane tube having an outer diameter of, for example, from 0.7 to 2.1 mm and an inner diameter of from 0.5 to 1.7 mm. It is not possible for the catheter tube by itself to enter the blood vessel.
Consequently, an inner needle member, which enables the catheter tube to enter the blood vessel, is detachably mounted in a front-end portion of the catheter tube in an insertion manner. The needle member is constructed of a hollow metallic tube having an outer diameter of from 0.5 to 1.7 mm, and extends from a front end of the catheter tube so as to pierce a wall of the blood vessel.
The needle member pierces the blood vessel's wall to enable the catheter tube to enter the blood vessel. After the catheter tube enters the blood vessel, the needle member is removed from (i.e., pulled out of) the catheter tube so that only the catheter tube remains or indwells in the blood vessel.
As described above, in the intravenous catheter set, the catheter tube is provided with the inner needle member therein, and is, therefore, naturally larger in diameter than the needle member. A conventional type of the inner needle member is constructed of a straight tube with a sharpened end forming a knife portion. Consequently, in a condition in which the needle member is mounted in the catheter tube in an insertion manner, as shown in FIG. 6, a front-end surface (i.e., cross sectional area) 12a of the wall of the catheter tube 12 forms an annular shoulder portion which extends radially outwardly from an outer peripheral surface of the needle member 11. When the needle member pierces the wall of the blood vessel, such shoulder portion or front-end surface 12a of the catheter tube 12 is resistant to the insertion of the catheter tube into the blood vessel.
Since the catheter tube is thin in thickness of the wall, it tends to have its front-end portion rolled back due to the presence of its shoulder portion 12a which abuts against the blood vessel's wall when the wall is pierced by the needle member 11. The thus rolled-back front-end portion of the catheter tube 12 is further enlarged in diameter and/or is torn, thus inflicting bodily and mental pain on the patient. Sometimes, the blood vessel is badly damaged by such diametrically enlarged and/or torn front-end portion of the catheter tube 12, which makes it difficult to continue the medical treatment of the patient.
Further, in piercing of the muscles and the wall of the blood vessel of the patient with the needle member of the catheter set, these muscles and blood vessels contract to increase their resistance to the shoulder portion 12a of the catheter tube 12, which facilitates rolling-back and/or tearing the front-end portion of the catheter tube 12.
Further, since the catheter tube made of polytetrafluoroethylene is poor in softness and flexibility, an inner wall of the patient's blood vessel is often damaged by the catheter tube and suffers from thrombophlebitis when the catheter tube is inserted into the patient's blood vessel. Furthermore, for example, in case that the catheter tube remains or indwells in the blood vessel of the patient's arm, there is a fear that the catheter tube may be broken when the patient bends his arm.
On the other hand, as for a catheter tube made of polyurethane, it is good in softness and flexibility but poor in smoothness. Consequently, a catheter tube made of polyurethane often permits the thrombocyte (i.e., blood platelet) to adhere to a surface of the catheter tube to produce the thrombus inside the blood vessel.
In a clinical test, it has been recognized that an allowable remaining (i.e., indwelling) time period for the catheter tube made of polytetrafluoroethylene in the blood vessel is 24 hours at maximum, and that of the catheter tube made of polyurethane is 48 hours at maximum.
Further, a surface in any of the catheter tubes made of polytetrafluoroethylene and that made of polyurethane is large in frictional resistance, and therefore gives the patient considerable pain when the catheter tube is inserted into the patient's blood vessel. Furthermore, it takes too much time and labor to pull the inner needle member out of the catheter tube due to its large pull-out resistance.
In the prior art, silicones are applied to the surface of the catheter tube to reduce its frictional resistance. However, nowadays, silicones have been found to be carcinogenic and are therefore prohibited from being applied to any medical instruments.